Dozens of children forced into prostitution were rescued in a three-day sweep of sex-trafficking rings, federal law enforcement authorities announced Monday.

The 105 victims, mostly girls, were rescued as the result of a coordinated effort that spanned 76 cities. The crackdown also netted 150 pimps, authorities said.

The largest roundups occurred in San Francisco (12 children and 17 pimps), Detroit (10 children and 18 pimps), Milwaukee (10 children), Denver (nine children and six pimps) and New Orleans (six children and six pimps).

"This operation targeted venues where girls and adults are operated for commercial sex, including streets 'tracks,' truck stops, motels, casinos, internet sites and social media platforms and the like," Ron Hosko, assistant director of the FBI's criminal investigative division, said at a news conference.

The ages of the victims ranged from 13 to 17, he added.

One of them was a 14-year-old Sacramento, Calif. girl who was found in Reno, Nev. during an investigation of an online posting for prostitution, the Associated Press reported.

Another 14-year-old victim was saved in Memphis after undercover officers found her through the website backpage.com. She named two men and a woman who she said forced her into prostitution, according to the Commercial Appeal.

Among three children recovered in Oklahoma City was a girl who'd previous been rescued during a raid last year in the Pacific Northwest, an FBI agent told the AP.

In Chicago, the FBI said it worked with city and suburban police to rescue two teenagers. A pimp and 96 johns were also taken into custody.

The nationwide sweep, dubbed Operation Cross Country, was the largest in the FBI's decade-old Innocence Lost initiative to combat child prostitution, the agency said. Its main partner in that effort is the National Center for Missing and Exploited Children.

With the most recent crackdown, the initiative has pulled more than 2,700 children out of prostitution, the FBI said.

Typically, cases start locally, with initial arrests leading to deeper investigations, led by federal authorities, of criminal networks that transport children and adults across state lines.

Some perpetrators are serving life terms in prison.

"Operation Cross Country demonstrates just how many of America's children are being sold for sex every day, many on the internet," NCMEC CEO John Ryan said in a statement.

Wendy Jolley-Kabi, executive director of the Association of Missing and Exploited Children's Associations, said her group, and the families they represent, reacted to Monday's announcement with a combination of sadness and excitement—sadness for the large number of children involved, and excitement that the issue of child sex trafficking is getting so much attention.

Many sex-trafficking victims go missing from the foster or child-welfare system, where there often aren't parents or advocates clamoring on their behalf, she said. Some of these kids are never formally reported missing, reflecting gaps in state laws.

Jolley-Kabi said she expects that in the next few days several active missing-child cases will be closed as a result of the recent sweep. But far too many cases will remain unsolved.